Some multi-band or other tactical radios operate in the high frequency (HF), very high frequency (VHF), and ultra high frequency (UHF) bands. The frequency range of these multi-band tactical radios is from about 2 MHz to about 512 MHz. Next generation radios will probably cover about 2.0 to about 2,000 MHz (2.0 GHz) (or higher) to accommodate wider bandwidths, higher data rates and less crowded frequency bands. Several standards have been developed for the different frequency bands. For HF, US-MIL-STD-188-110B and US-MIL-STD-188-141B specify waveforms and minimum performance requirements of waveforms and radio equipment, the disclosures which are incorporated by reference in their entirety.
UHF standards, on the other hand, provide different challenges over the 225 to about 512 MHz frequency range, including short-haul line-of-sight (LOS) communication and satellite communications (SATCOM) and cable. UHF waveforms operate through different weather conditions, foliage and other obstacles making UHF SATCOM an indispensable communications medium for many agencies. Different directional antennas can be used to improve antenna gain and improve data rates on the transmit and receive links. This type of communication is typically governed in one example by MIL-STD-188-181B, the disclosure which is incorporated by reference in its entirety. This standard specifies a family of constant and non-constant amplitude waveforms for use over satellite links.
The joint tactical radio system (JTRS) implements some of these standards and has different designs that use oscillators, mixers, switchers, splitters, combiners and power amplifier devices to cover different frequency ranges. The modulation schemes used for these types of systems can occupy a fixed bandwidth channel at a fixed carrier frequency or can be frequency-hopped.
These systems use many different types of modulations, including M-ary phase-shift keying (M-PSK) modulation, M-ary quadrature-amplitude modulation (M-QAM) or modulations with memory, such as continuous phase modulation (CPM), and are sometimes combined with convolutional or other type of forward error correction codes. To ensure interoperability, standardized waveforms are often used. These and other systems often use a Binary Phase Shift Keyed (BPSK) waveform for Demand Assigned Multiple Access (DAMA) communications systems. Some examples are the 117F and F3 manpack radios manufactured by Harris Corporation of Melbourne, Fla. Several performance issues were noted in some of these and similar radios as caused by “bad” acquisitions. The receiver modem must acquire the waveform in each DAMA slot such as corresponding to a time division multiple access (TDMA) slot. If acquisition estimates have excessive error, data is lost for the entire slot.
This type of modem often uses a Fast Fourier Transform (FFT) to detect the waveform and exploit spectral characteristics of a transmitted preamble. After the modem processes the FFT and detects the preamble, the modem estimates the frequency offset and the phase from complex FFT output values. It is desirable to improve acquisition estimates of the frequency offset, phase error and symbol timing to allow better processing and acquisition estimates and enhance communications.
Also, because of the non-random aspect of the preamble, the start of message bit correlation can sometimes false alarm during this non-random preamble portion of the waveform, i.e., the 110110110110 portion of the preamble, for example, forming the training sequence. It would be advantageous if false detections could be reduced in this portion of the preamble prior to the start of message bits.